Recovery of tar acids from tar



Ma 12, 1935. 5 MULLER 2,040,09

RECOVERY OF TAR ACIDS FROM TAR Filed Aug. 6, 1929 2 Sheets-Sheet l Z4 l 6 /7 F19: .Z- 3 20 /7 7 a I? w 7 1 J l I /f Z04 lQ VENTOR g ww 74M ATTORNEYS ay 12, 1936. I s. P. MILLER 2,@40;096

RECOVERY OF TAR ACIDS FROM TAR INVENTOR- WW a; fim

ATTORNEYS Patented May 12, 1936 UNITED STATES. PATENT OFFICE RECOVERY OF TAR ACIDS FROM TAR Stuart Parmelee Miller, Englewood, N. J., as-

signor to The Barrett Company, New York, N. Y., a. corporation of New Jersey Application August 6, 1929, Serial No. 383,859 10 Claims. (Cl. 260-154) This invention relates to an improved process in the recirculation process. When air is emfor the recovery of tar acids from tar, whereby ployed, any oxidizing effect which it may exert the tar acids can be recovered directly from the will be limited to the preliminary period of re01rtar instead of from distillate oils produced from culati n. Similarly, fu l when used in an 5 the tar. unpurified state, will be purified during the early r The common method of recovering tar acids or stages of the process h t e s s phenols from tar is to distill the tar and extract u a d Ov r and Ov ageln. y Such t d the tar acids from the distillates with a caustic t na am u t of as n d be ad d as s q d soda solution. A large amount of distillate must to m p f r l s s nd f h gases a y be handled in most cases to produce a relatively be d wn O m. t e Ci ulat ng sy t m: 8. small amount of tar acids. Where the tar acids through Conde sers- Whe the Process 8 not are extracted at a plant remote from the tar disoperated s a e u t n p s, e as s a d tillation lant, the cost of transportation of the ad x d oil v after t extraetlon of r distillate oil is an added expense. Tar acids cand p an be c d t d s any n t al not be directly extracted from tar with caustic oils which m b carried b the s s. So also,

soda solutions in a satisfactory manner. When the gases are recirculated, the admixed The present inventio provides an improved gases and oil vapors leaving the caustic soda abprocess for recovering tar acids from tar whereby i may be Somewhat cooled to condense the tar acids can be directly recovered without tral Oils therefrom, and the gases then reheated the, necessity f producing large amount of for further use in the reclrculatory process. The distillate oil an Washing or extracting such vaporization of tar acid oils from the tar will result tillate oil with ca ti soda, Somtions. in vaporization not only of tar acids or phenols,

According to the present invention, inert gases but also of Varying amounts of neutral 011$ or vapors are as d th or t intimate hydrocarbons which will remain as vapors unless contact with the tar whileit is inaheated condicondensed from t admlxed gases by etion to eifect vaporization of tar acid oils, and the If Such Condensatloh does o take P t a d 1 resulting d ix d gases and apors are brought the gases and admixed vapors are recirculated, into contact with an alkaline solution, e. g. a caus the recirculated gases and Vapors W111 be made up tic soda solution, to extract the tar acid vapors. in part of inert gas and in e of neutral Oil The inert gases, after they have been employed Vapors- Part of the neutral 011 Vapors can be for the vaporization of tar acid oils and after the. condensed and neutral oil recovered by cooling tar acid vapors have been extracted by the causthe recirchlafihg gases or by drawing ofipart tic soda solution, can advantageously be recircuof the admixed gases and Vapors from the lated through the tar in a cyclic manner and emlatihg system and supplying additional inert ployed over and over aga n for vaporizi t acid as required. Or the process may be operated so oils from the tar, followed by extraction of tar that the gaseous le s medlum conslsts acid vapors from the admixed gases and vapors. tirely 011 Vapors malhtamed above their In such recirculation process, the tar and the dehsahoh temperaturecaustic solution can both be kept at the same or The tar which is Subjected the dephenolizing 40 si ila temperature and t gases can be treatment should be heated to a suitable temcirculated through insulated lines so that the en perature, for example, somewhat above 0., tire operation is carried ut with minimum of before the inert gases are brought into contact heat loss and with the circulating gases maintherewith, aIthOUJgh this Will depend p n t e tained at a uniform temperature, or at temperaquantit f as r u a d p t f ar acids culation. quired temperature by the use of a steam pre-,

The inert gas or vapor which it is considered heater or by e u of w e t m t e flue particularly advantageous to employ in the presgases in the flues at coke or gas plants, or by ent process is steam which, at temperatures above the use of waste flue gases from tar stills, steam 9 its condensation point, acts as an inert gas or boiler plants, etc., 01 by the s Of eat ntervapor, and can be passed through the tar and changers in which hot tar or pitch is employed through the caustic solution and recirculated at as the heating medium, or by separateheating such temperatures without condensation, or withstills, etc. out any considerable condensation. Air or inert Where the recovery of tar acids from the tar gases such as nitrogen, fuel gas, etc. may be used is carried out at coal distillation plants at which 2 coal tar is produced, such as coke oven plants or gas plants, the tar separated from the gases at an elevated temperature, may be kept hot and employed in a heated condition. In many cases the temperature will be sufficient for carrying out the tar acid removal process without added heat or at least without any substantial amount of heat. Where the collector mains of a coke oven plant are operated at high temperature with the use of hot tar for flushing the main, the hot tar drawn ofi from the main may be at a sufficiently high temperature so that it does not require further heating, and so that it can be led directly from the main' to the apparatus for the removal of tar acids.

In the distillation of tar, where the tar must be heated to a high temperature, the removal of tar acids according to the present invention, can advantageously be combined with the distillation, for example, by passing a current of inert gas through the tar after it has been preheated to the proper temperature and before it is subsequently'heated to a higher temperature for the main distilling operation. In the case of an ordinary tar still'containing a large batch of tar, the still can be heated unt'l the tar is at the proper temperature and inert gas can then be circulated through the tar, and the resulting gases and vapors passed through the caustic soda solutionand the gases recirculated until the tar acid oils have been driven off to the desired extent, after which the recirculation can be stopped and the'still heated to a higher temperature to effect distillation of the dephenolized tar. the tar is distilled in a pipe coil still with heating of the tar in a pipe coil and discharge of the heated tar into a vapor box or vapor separating chamber, the initial heating of the tar can be so regulated that the tar will be at the proper temperature in the vapor separating chamber and current of inert gases can be passed through the tar in s ch chamber to remove tar acid oils, after which the dephenolized tar can be heated to a highcr temperature by circulation through another pipe coil which discharges into another vapor separating chamber, etc.

For effective removal of tar acids from the tar, it is important that the inert gas or vapors should come into intimate contact with the tar. This can be accomplished in s table scrubber towers or other types of scrubbers. Any suitable type of scrubber or dephenolizer may be used so long as it provides intimacy of contact between the tar and the inert gas. A scrubber such as a well packed tower which provides for satisfactory degree of countercurrent contact, is well suited for use. Scrubbers in which the tar is sprayed or atomized into the inert gasmay also be employed, but in such case it will usually be desirable to recirculate the tar or repeatedly spray or atomize it into the gas in such large volume as will bring all parts of (he tar'into contact with the inert gas so that the tar acids and attendant oils may be vaporized therefrom. Less efficient types of scrubbers can be employed, and, where the re moval of tar acid and oil vapors with inert gas is combined with distillation of tar, the inert gases can be passed through the tar still, in the case of the still containing a batch of tar, or through the vapor box of a pipe coil still, etc.

The scrubber r extractor employed for removing tar acid vapors from the mixture of gases and vapors may be of any suitable type, such as the types mentioned in connection with the tar scrubber, or the gases may be passed through caustic solution in a tank. Those parts of the extractor with which the caustic liquid comes in contact should be constructed of a caustic-resistant material.

The removal of tar acids from the tar can be carried to the point where the tar is practically completely stripped, or nearly stripped, of tar acids, or to the point where only the lower boiling acids, e. g. the phenols and the cresols are removed and recovered. A partial removal of the more readily vaporizable tar acids can be effected without removing the higher boiling and more difiicultly removable acids. So also, the removal can be carried out in stages, for example, by passing the tar through a series of scrubbers where it is scrubbed by the inert gas, and with recirculation of the inert gas from one scrubber through the tar acid absorber and. back to the same scrubber. In such multi-stage extraction of tar acids, the carbolate solutions produced will vary from each other, the carbolate solution from the first scrubbing operation giving a carbolate richer in lower boiling tar acids, while those from the successive scrubbing treatments will give carbolate solutions richer in higher boiling acids.

The tar subjected to the dephenolizing treatment of the present invention, may be ordinary coal tar from coke oven or gas retort plants, or it may bea heavier tar fraction or a lighter tar fraction, such as the heavier tar collected from the collector main of a coke oven plant, or the lighter tar or tarry oil recovered in the condensing system of a coke oven plant. Tars from various gas retort plants, including vertical retort plants, and low temperature tar, etc., can be subjected to treatment for the recovery of tar acids therefrom, according to the present process. In many cases, particularly at coke oven plants, it will be of advantage to treat only the lighter tar or tarry oils separated in the condensers, since this lighter tar contains a much higher proportion of tar acids than the heavier tar separated in the collector main. The lighter tar from the condensers may represent only around 25 to 35% of the total tar, yet itordinarily contains around 50 to of the total tar acids.

When employing the recirculation process of the present invention, the only oil removed from the recirculating gases, in addition to the tar acids absorbed in the caustic solution, will be the oils dissolved in the carbolate solution, or such as may be condensed in the caustic absorber. Neutral oil vapors will be formed or separated from the tar during the recirculation of the gases, but these neutral oil vapors will be carried back with the inert gases through the tar where the oil vapors may be in part reabsorbed, or where their presence will retard and limit the further vaporization of neutral oils, resulting in a selec tive vaporization of tar acid oils from the tar. In such case, the recirculating gases will be admixed with neutral oil vapors. Since neutral oil vapors will be carried in the gases, in such recirculatory system, such neutral oils may be recovered from the circulating gases, after they have passed through the tar acidabsorber. In such cases, the caustic scrubber or tar acid absorber may be followed by fractional condensation to condense part of the neutral oil vapors. Naphthalene oil vapors may be recovered in this manner.

The rate at which tar acids can be removed from the tar depends upon several factors, e. g., the temperature to which the tar is preheated, the relative volume of steam or other inert gas and partially it leaves the scrubber.

It may be desirable also to somewhat cool the dephenolized and passage through the caustic absorber. If cooled prior to passage through the caustic, the oils condensed will contain tar acids and should, if maximum recovery of tar acids is desired, be

distilled tar.

Oil vapors will in many cases serve satisfactorily as the gaseous medium employed for removal of the tar acids from the tar. This will particularly be the case with tars containing lower boiling oils, e. g., tars containing benzol, toluol and the xylols. By heating the tar to the point at which these lower boiling oils are vaporized, the vapors may be recirculated through the tar and the caustic solution. These oil vapors serve as the inert gases employed in my process.

Where waste steam is available, such as exhaust steam, or where steam is otherwise available at suf iciently low cost, the process can be carried out as a steam distillation process without recirculation of the steam. In such case, the steam will be passed through a suitable scrubber tower or other device for driving off tar acid oil vapors from the hot tar and the admixed vapors and steam will then be passed through a caustic scrubber to remove the tar acids after which the steam leaving the caustic absorber may be condensed, together with the neutral oil vapors, and the neutral oils recovered as a condensate. These neutral oils, recovered in this way, may be kept separate, or may be returned to the tar.

In carrying out the recirculation process, the recirculated steam or other gas or vapor may if excess caustic soda until the. absorbing capacity of the solution is exhausted or reduced to the desired point.

In some cases with relatively high temperature in the tar scrubof caustic in the second or upper stage. In this way, the caustic solution can be exhausted of caustic soda and at the same time the tar acid vapors extracted with substantial completeness from the gases.

A selective extraction of the phenols or tar acids from the admixed gases and vapors can be eration in stages. If, for example, a carbolate rich in phenol and a second carbolate rich in higher boiling tar acids, including cresols, is deadditional gases carrying phenol and higher phenols will result in the driving off of higher phenols and the absorption of phenol until the carbolate solution in the lower section will be greatly enriched in sodium phenolate, while the higher phenols will be absorbed in the higher section. With a multi-stage operation of this kind, it is possible to produce carbolates predominating in phenol, the cresols, the xylenols, etc. If still more selective extraction is desired, the carbolate absorber may be constructed in a larger number of stages, e..g. five or six, and a plurality of different tar acid fractions obtained.

The recovery of tar acids from tars, according to the present invention, may be carried out batch-wise or continuously, that is, from successive batches of tar, or from tar which is continuously supplied and with continuous discharge of the dephenolated tar, and likewise with batchwise or continuous operation of the caustic soda absorber, using successive batches of caustic soda solution for forming phenolates, or supplying additional fresh caustic continuously and withdrawing the carbolate solution continuously. With batch-wise operations, the caustic absorbers may be installed in parallel or at least in duplicate with piping arranged for allowing saturated carbolates to be produced first in one and then in the other absorbers. At tar distillation plants, particularly at continuous tar distillation plants, with continuous supply of tar to the dephenolizing scrubber, the system of dephenolizing can be made a part of the distillation unit, so that it will function continuously and require no labor in addition to that normally required for ,the continuous distillation.

At plants employing continuous pipe coil stills, with heating of the tar in a pipe coil, or in a series of pipe coils, which discharge into vapor separating chambers, the dephenolizing scrubber may be one of the vapor separating chambers and the dephenolizing operation can be carried out continuously as a part of the continuous pipe coil still distillation, using the tar when it has been heated to the proper temperature for the dephenolizing treatment and subsequently heating the dephenolized tar to a higher temperature to complete its distillation. In such a case, the steam or other inert gas would be recirculated from the vapor separating chamber or from the still through a caustic scrubber, and the steam and admixed gases then cooled to separate neutral oil, or recirculated. In such operations, steam may or may not be employed, and it may be found desirable to use a vacuum in some cases, although the process may, if desired, be worked under pressure. Where the removal of neutral oils along with the tar acid vapors is sufiicient to leave a pitch product which does not require further distillation, the neutral oils can be recovered from the gases after leaving the caustic absorber. So also, where such a pitch is produced, the neutral oils can be returned to it after the extraction of tar acid vapors, thus giving a tar of similar composition to the original tar except for the removal of tar acids therefrom.

The invention will be further described in connection with the accompanying drawings, which are in the nature of flow sheets and are more or less conventional and diagrammatic in character and which illustrate various arrangements of apparatus for carrying out the invention, but it will be understood that the invention is not limited thereto.

In the accompanying drawings,

a heating furnace or I Fig. 1 shows 'one system of apparatus adapted for carrying out the invention;

Fig. 2 shows a modified system in which multistage extraction of the tar is provided for;

Fig. 3 shows an apparatus having a condenser arranged in the recirculating gas line to condense neutral oils from the recirculating gases; Fig. 4 shows a simple fire-heated still combined with apparatus for recovering tar acids directly from the tar in the still;

Fig. 5 shows a two-stage absorbing tower;

Fig. 6 shows an apparatus with a three-stage absorption tower for fractionally extracting phenols; and

Fig. '7 shows the invention combined with a pipe coil still for distilling tar continuously. In the various figures, the corresponding parts are indicated by the same reference numerals, in some cases with reference letters appended thereto.

Referring to Fig. 1, tar from a suitable storage tank I is pumped by pump 2 through the line 3 to a preheater comprising a pipe coil 4 arranged in chamber 5 and heated by waste heat or otherwise. The preheated tar passes through the line 6 to the top of a scrubber l in which the tar is subjected to a countercurrent flow of steam or other inert gas. The tar after the dephenolizing treatment passes through the line B to a place of storage or to distillation equipment, etc.

The scrubber I may be a tall packed tower which provides for intimate contact of the tar flowing downwardly therethrough and the gases passing upwardly therethrough. The packed section of the tower is indicated at 9. A current of steam or other gas is forced by blower 10 through line I l to the bottom chamber l2 at the bottom of the scrubber tower and passes upwardly through the packed section 9 to the chamber 13 at the top of the tower from which the gases and vapor pass through the line M to the bottom of a dephenolizing tower l5 and pass upwardly therethrough countercurrent to a caustic soda solution. The gases freed from tar acid vapors escape through the line 16 and may be recirculated by the pump lil. Where the gases are not recirculated, they may be drawn off through the line 24 and fresh steam or other gas supplied to the blower It! through line 50, or any of the gases and vapors can be led out through the line 24 and the remainder recirculated and make-up gases admitted through the line 50. Fresh caustic solution is supplied to the top of the dephenolizing tower l5 through the line H and provision is made for drawing oif the phenolate solution from an overflow l8 at the bottom of the tower. Provision is also made for recirculating the caustic solution through the circulating line 29 by means of the pump 2| and discharging it at 22 into the top of the tower. A heat interchanger 23 is shown in the line 20 for use if desired to heat the circulating caustic solution to maintain it at the proper temperature, or, where the gases and vapors entering the tower are at a much higher temperature than the caustic solution, the solution may be cooled in the heat interchanger to avoid too great evaporation of water from it by the hot gases. The carbolate solution is collected in receiver l9. The tar acids or phenols can be recovered from the carbolate, for example, by treating with carbon dioxide which sets free the tar acids or phenols and forms sodium carbonate which can be recausticized for further use in the process.

desired portion phenolizing treatment Theappa'ratus of Fig. 2 is similar to that of Fig. 1 but provides a two-stage dephenolizing treatment in which the partly dephenolized tar escaping from the first dephenolizing scrubber 1 and vapors are returned through the blower l0 and the line I I to the scrubber 1.

In Fig. 4, a simple fire-heated still is shown at 1 with provision for forcing steam or other gas through the body of hot tar in the still. The resulting gases and tar acid oil vapors pass through the line I4 to the bottom of the caustic scrubber IS. The gases and vapors escaping from the top of. the tower pass through a condenser 25 at a regulated temperature, the condensate collecting in the receptacle 26 and being drawn oil therefromwhile the uncondensed vapors and admixed gases return through the line 21 to the blower 28 through the perforated pipe 29 of the body of hot tar in the still. When the tar has been heated to a suitable temperature, e. g. around 100 C. or somewhathigher, steam or other gas is forced through the body oftarto remove tar acid oil vapors and the resulting vapors and gases pass through the caustic absorber, then through the condenser to condense part of the neutral oil vapors and the uncondensed vapors and admixed gases are then returned for recirculation to the still. After the tar, acids have been driven off to the desired ex- ,tent,;the recirculation can be discontinued and the still heated to a higher temperature and the distillates carried over through the line 5| to the ,QOndenser 52. In this case, more or less of the light neutral oils can be recovered during the deand drawn off from the receiver 26, while the oils subsequently distilled from the tar will be collected in the usual way by condensation in the condenser 52. In Fig. 5 a two-stage caustic scrubber is shown in the form of an upper and lower section I50 and -I5b,-separated by a collecting plate 30, through which the gases and vapors are permitted to pass upwardly and through which the caustic solution can overflow from the upper to the lower section. 'In' this tower, the caustic solution is supplied to the .top of the tower and the carbolate solution .drawn oil from the bottom. Provision is made 'for recirculating both the caustic solution and the carbolate in the respective sections of the tower, while the excess will overflow from the top to the bottom section. The gases laden with tar acid oil lvapors will enter the lower section and may completely saturate the caustic solution with carbolate. The removal of tar acid oil vapors will becompleted in the upper section to which fresh caustic soda solution can be continually supplied.

The apparatus of Fig. 6 has a three-stage absorber so that, for example, carbolates predominating in phenol, the cresols, the xylenols, etc.

' is made for supplying fresh caustic both to the upper section l5d and to the lower section I51 and for drawing ofi .carbolate solution from the bottom of the middle section and also from the bottomof the lower section through outlet lines intermediate compartment I 56 will be operated in the same manner except that the caustic stream supplied through the pipe He will enter higher boiling acids. With a larger number of stages, a more selective extraction of the tar acids can be obtained by proceeding in a similar manner.

In the apparatus of Fig. 7, the dephenolizing tower is arranged between it can be pumped by the pump 40 through the line 8 to the heating coil 4| and there heated to a high temperature and then discharged into the vapor separating chamber 42, from which the pitch is withdrawn through the outlet 43 to a receiver 46 while the oil vapors distilled from the tar pass through the line 44 to the water con- .denser 45 and are collected in receiver 41. The heat supplied to the tar for preheating it prior to dephenolizing, is employedin the subsequent further heating of the tar so that, in the subsequent heating, it is only necessary to heat the tar from its preheated condition to that to which it is to be subjected for the final distillation. The dephenolizing treatment in this case is combined as a part of the pipe coil distillation, so that the tar is dephenolized after it is preheated and before it is further heated for. the main distillation.

In the diagrammatic drawings, heat interchangers or heating devices for thecirculating gases and for the circulating caustic solution are omitted, except for the heat interchanger shown in Fig. 1. So also, the means for heating the tar or for supplying hot tar is omitted in all of the figures except Figs. 1, 4, and 7. It willbe understood that the tar will be employed in. a suitably heated state, or will be preheated in some suitable manner, as hereinbefore pointed out, and that additional heating or cooling of. the circulating gases and of the carbolate solution may be employed, and that, in those f gures ,whichshow recirculation of the' gases without provision for the supply of fresh gases and the withdrawal of part or all of the gases, additional gases may be supplied as required, and part or all of the gases can be withdrawn instead of being recirculated, in which case the withdrawn gases and vapors will be cooled tocondense the oils therefrom.

The further treatment or disposal of the tar, after the dephenolizing treatment, is not shown except in the case of Figs. 4 and 7, but it will be understood that the tar which is in a heated condition as it leaves the dephenolizing scrubber can be passed to a tar still to be there distilled so that its contained heat can be utilized, or that the tar can be otherwise disposed of. At tar distillation plants, the present process can advantageously be combined with the distillation process by subjecting the tar to a dephenolizing treatment after it has been heated to the proper temperature and before it is further heated for further distillation. The temperature to which the tar is heated before it is subjected to the dephenolizing treatment can be varied, depending upon the pressure under which the scrubber is operated, i. e. whether at atmospheric pressure, under increased pressure, or under a pressure lower than atmospheric, the volume of inert gases circulated through the scrubber or still, the extent to which the higher tar acids are to be driven off and recovered, and like considerations. Where steam is employed and circulated or recirculated through the tar scrubber, it will be evident that the temperature of the tar should be above the temperature of condensation of the steam, and that the temperature of the caustic scrubber should also be above the temperature of condensation of the steam. It is desirable, although not entirely necessary, to maintain the caustic scrubber and the tar scrubber at the same or similar temperatures, particularly where the gas is recirculated repeatedly through the two scrubbers. The maximum temperature of the gases and vapors leaving the caustic scrubber will be limited by the presence of caustic solution which will tend to cool the gases and vapors to a temperature approximating that of the solution. Temperatures of the tar in the tar scrubber and of therecirculating gases of around 125 to 175 'C. are suitable, although the temperatures can be materially lowered when the process is carried out under reduced pressures or with the use of inert gases other than steam. At lower temperatures the volume of steam or other inert gas recirculated must be increased per unit quantity of tar acids recovered.

The present process has the advantage, among others, of giving the tar acids directly without the separate recovery, shipment and extraction of a large amount of oils, thus making unnecessary the provision of large carbolic oil storage and extraction systems. The process also enables tars to be treated for the recovery of higher percentages of tar acids than can be economically recovered by present day processes due tothe troublesome handling of higher boiling heavy oils. The process also yields carbolates and tar acids 'of high quality, low in sulfur compounds and low in distillation residue, while it enables caustic losses to be reduced to a minimum and enables equipment required to be materially reduced. The process is also of value for recovering tar acids from tar acid oils, particularly those which are contaminated with tar. With low tars or tarry oils, which are unusually high in tar adds, the present process enables a high yield of the tar a'cids'to be recovered directly from the tar, and with fractional separation of higher and lower boiling acids, if desired.

It will be understood that variations and modifications can be made in the process as hereinbefore described, without departing from the spirit and scope ofthe invention.

I claim:-

1. The method of recovering tar acids from tar, which comprises passing inert gases into intimate contact with hot tar to efiect vaporization of tar acid oils, and effecting selective and frac tional extraction of tar acids from the resulting admixed gases and vapors by passing the same through a series of alkaline solutions and regulating the solutions to effect selective and fractional extraction of the tar acids from the admixed gases and vapors.

2. The method of extracting tar acids from admixture with inert gases in vapor form, which comprises passing the gases into the first of a plurality of chambers and then thru the other chambers in series, removing the extracted gases from the last of the chambers, introducing fresh caustic into the last chamber, supplying the otherchambers with caustic mixed with carbolate formed by action of caustic on the tar acids in the gases, recycling a portion of the carbolate through the first chamber and withdrawing carbolate from the first chamber.

3..Ifhe method of extracting tar acids from admixture with inert gases in vapor form, which comprises continuously bringing into contact with the gases a solution comprising caustic and carbolate recycling at least a portion of the resulting solution and adding fresh caustic to the recycled solution.

4. The method of extracting tar acids from admixture with inert gases in vapor form, which comprises extracting the tar acids by an alkaline solution recycling at least a portion of the alkaline solution for further extraction of tar acids and increasing the temperature of the solution before reuse.

5. The method of extracting tar acids from inert gases in vapor form, which comprises con-'- tinuously introducing into a chamber through which a mixture of the tar acids and gases are passed, fresh caustic solution and reused solution containing carbolate, withdrawing the resulting solution and reusing a portion in the chamber for the extraction of tar acids.

6. The method of extracting tar acids from admixture with inert gases in vapor form, which comprises producing a carbolate rich in phenol by bringing into contact with the gases and tar acid vapors a caustic solution containing .an amount of caustic not in excess of that required to neutralize all of the phenol and then extracting higher tar acids from the resulting mixture of gases and vapors by bringing an alkaline solution into contact therewit 7. The method of selectively absorbing tar acids from a mixture of vapors comprising phenol and higher tar acids which comprises passing said vapors incontact with a caustic solution containing insufficient caustic to combine with all of the tar acids in the gas contacted therewith, passing the thus treated gas in contact with a second caustic solution to separately absorb tar acids unabsorbed by the first caustic solution, whereby phenol and higher tar acids are selectively absorbed in said caustic solutions, and separately withdrawing said caustic solutions from contact with said vapors.

gether with neutral oil vapors into contact with the tar.

withdrawing liquid residue therefrom, an extracmaterial.

STUART PARMELEE MILLER. 

